Method of grinding butt joints of wound cores



y 1943- J. H. BRAMBLE ET AL 2, 8,052,

METHOD OF GRINDING BUTT JOINTS OF WOUND CORES V Filed April 15, 1941 S i v l V ENTOR S j fi/am aka WITNESSES:

Patented- May 4, 1943 UNITED" METHOD OF EST-AT ES GRINDING Burr JOINTS F WOUNDjCOBES JohnH. Bramble, Sharpsviile, and Michael'Dunn,

Sharon, Pa., assignors to Westinghouse Elec trio 8% -Manui'acturing"Company, East Pittsfl burgh, Pa-.,- acorporation of Pennsylvania r Application April- 15,1941,,SerialNdhSSilfiilOl;

' 9Claims (015511- 135).

This invention relates to the workingo'f' the faces 'of sheet steellaminations thatare bonded together and ent toform butt joints in a magnetic structure of induction apparatus, such as transformers.='- Recent developments inimagnetic steel have'produced steels having very good magmethodjbf grinding tended to separate the lami I nations one from the other,*that-is, -to split or destroy the bond betweenthe laminations.

Ithas been found that when the joint is ground neticpropertiesof'low loss and high permeability in the direction "in which the material is rolled during its process of manufacture. .To obtain the maximum benefits from-the use'of' such material, it is neces'sary to use it in such mannerthatthe .lines of magnetic flux, that is the-direction of magnetization, coincides substantially with the direction of rolling the 'materialduring its process of manufacture.-- I

Core structures have beenvdeveloped in which the-direction of magnetization coincidesthroughoutwith the direction of rolling by forming the core loops of a'continuous strip'or ribbon or steel slit to the proper width and wound tov a predeby m'ovement of the abrasive .sur faceof the belt I across the several,laminations thatgis, so. that the belt moves .frompne lamination to "the next v or atright anglesto the planesof the laminations as they contact thejlbelt instead of parallel etchings when the grinding ,is done by movement of theabrasive surface across the laminato the edges of the laminations contacting the belt, a fiatterground-suriace is produced and the burrs are .much more readily-removedby tions insteadof in thedirectionof the laminations, the resulting burrs from, each lamination e are allon the same side of the several laminations,

r tel-mined thickness of the material on a mandrel of such'lshape as to give the desired window 1 The core loops so formed areannealed to re i lieve strains in the material caused by the wind- 7 ing operation and are then impregnated with there being a burron one side only of eaclrlami nation instead 'of on 1 both sides *asi when the grinding surface passes along the edge 10f the lamination Itis an object of :the I invention to. provide for grinding-the surfaces :on theopposite sides of-a.

' butt joint in: a laminated sheet steel core structure, the severallaminations of which are bonded together to ,prov ide asmoo thflat joint surface.

bonding material and baked to bond the several layers of magnetic material solidly together. In

order to provide for assembling the wound core loop structure aboutform-wound copper coils of the electric circuit, the"core loops are cut to form two U-shaped parts and the butt Joint surfaces formed by this cut are worked by grinding and etching to'provide a'flat surface free fror'nshort circuiting burrs. v

It has been found that'for grease the butt joint surfaces on this'type of core structure, a

water cooled abrasive belt grinder consisting of a continuous belt produces the best surface in the shortest grinding time. It had been the'practice when grinding the surfaces on this type of grinder to rest the core parts against a bridge type of Otherobjectsiand advantages r th raw-er ata will be apparent from the following description" .ofoneembodirnent thereof, reference being had to the accompanying drawing, iny'vhich:

Figure 1 is a side elevationalview partly in section of apparatus arranged for grinding the s laminated core parts. i

stop so'that the planes of the laminations' being ground were parallel to the direction of movement of the abrasive-belt. It was soon found, however, that this method of grinding was critically related to the stralghtness or flatnessof the cut surface before grinding, The belt life was found to be good only when extremely close tolerances were maintained during the cutting or sawing operationy It was alsofound that the core parts could stand only a very limited amount of grinding ina direction parallel to the planes of the laminations without'producing thick burrs that become dimcult to etch, and also that this Fig. 2 is a perspective viewof a portion of the pparatus shown in Fig. .1.

F1g.-3-is a top plan view of the parts of the apparatus shown in Fig.-2, and l I Fig. 4 is an enlarged 'elevational showing the burrs formed by' grinding.

Referring to the drawing, a tank i isprovided I for collecting water from an endless abrasive belt 3 which travels over the rolls 4 and 5 the upper fiat portionof which travels over a flat table 8 positioned under1the smooth sideiof the abrasive belt and which may be supported 'from the side walls of the tank [by brackets a. A u- 7 view'of the ends of the laminationsat the joint surface the other so that each layer extends about thespaoe between twoparallel legs 13 and It, the

ing, less heat is evolved ground and the life of the belt is much greater ends of whichiaretcut and ground [tofform the; surfaces ofa'butt joint when two similar core parts II are positioned together to form a com- 7 TWO bridg typ stops Provided for engasing the two leg -of thereon! in:

plete magnetic loop.

than when the structure is ground by movement of the belt parallel to the edges of the lamination.

Modifications in the apparatus'and in the details of, the method of grinding disclosed may be made within the spirit of the invention and we do". not wish to be -limited; otherwise thanv by the scope f the appended claims. '1

part being ground over a narrow surface closely-j. adjacent to the traveling belt}. .One. stpp I5 is rigidly fixed. as by handwheel operatedflscrews it,

to the table top-8 and the core-part Ii is posii tioned to straddle this bridge rest o that itwill rigidly bear against the first of the two legs i3 We claim as our invention: w

*1. Apparatus for working the outer end surfaces of U-shaped core portions formed of a pluralityof laminations of magnetic sheet steel positioned fiatwise and bonded t ether, the one upon the other about the space between the two legs of "lthe' u shap ed coreiportion, comprising means for positioning the U-shaped core portion in engagement with a'movable fiat grinding surface with to be engaged by the traveling belt 3, which is indicated by the arrow, as moving from the left toward the right in the several views. The sec- 0nd ibridge rest-"stop I1 is yieldably mounted a with respect to a bracketlt'thatis attached to the table""'top l'kby handwlie'el operated screws l finto recesses which spring members 2 0 are" provided roasts permit a; certain amount of I yieldabie motion of the member I "-4 -A supply-ofwat'er is provided through pipe 2 i, the lower part. having two branch horizontal end portions 22 and. 21 from he undersideof which water is supplied the ends otthelaminations in engagement with the grinding surface substantially at right angles tothe'di'rection of motion of thegrinding urface and including means for supporting thepol' zP rtioncomprising a pair of narrowlow fixedbridge rests,- :close1y a ja ent to thegrinding surface, the

bridge rest for. supporting i one leg of thecore porttion being rigidly fixed in position. i to, 'prevent to 'the surface of the abrasive belt I. The portion v I face o :s P d or P rti s io mes lota D1:

i lfjeirt'ends-alonga recess 24 in the rest |5., "A. mo or 25 or 'other'fsuitable. driving means is pro 'vided'and "connected through any suitable driving to rotatethe'rolls l and 5 and carrythe belt I in a clockwise direction sothatzthe DOr-Q tions engaging the surfaces being "ground traverse from left toright, -"as viewed in-the' drawing. .The

belt traverses at'a very high speed .such as:'700.- feet p'er'm'inute 'an'd carrieswater for coolingthe belt and aiding in the'grinding operation from the lower part of the tank Ito the first leg ll'to be.

ground; the water-supplied through-the pipe 23 maintaining the abrasive belt moist as it. passes:

under t-h'e second leg of the core structure; I

It "has been found that in-pro'viding the two bridge rests I 5 and i I; the first of "which is rigid a'ndf' tlisecond of which yieldably-engages the leg ll thata certa'in amount of spring in the core part being-ground m'aytakeplace without injuring tl'iestructure whereas if both legs of the core 1y at. right angleste the direc ion of motion of structure are rigidly braced against bridge' stops, I

.Droducing-a very fiat surfacee. 1; it

As shown in Fig. 4, the layersllof magnetic material-mare spaced apart slightly by bonding material in the spaces and thevburrs .21 that are formed byethe action of, the-vabrasive belt 3 appear only on one side of, each of the. lower surfaces of; the laminations 12 ,which are thinner and-thus more v readily;- removed; than" when r the belt travels in the direction alongtthe surface of thelaminationsinsteadpfacross them- {The amount of. material that mllst then be removed by etchingis smallsand the time required for the etching operation-is correspondingly reduced. I :s nc fl hor es -d m n ion e t ur a inss eund s ra el o t e wa a p dother coreleg.

movement of the supported leg; with thegrinding'. surface, .and the -bridgerest fon supporting ,the; other leg of the core portion being yieldably biased against the other core leg,

e m s for, we i .sit i kl tt el xof mi at n of a ne ic s sts e P T-1 i n d twi and-b nd d :tpaefl uthe o e upon the other about the-,space between the two legs of the U-shaped core portlon, comprising means for positioning the UaSMDd coreportion in engagement with a movable fia t grinding; sure ththe 1 1 2 1, h e amin i sj a 'n gagement-with the grinding surface substantialg h rin i Su ia e :anf i i c u naimeaeafqrsup orfl a hes re. q t a fi m vi a pai o narrow low fixed bridge rests, one of said rests xertin ,aJigid resistance againstmovem'ent of one core leg andthe-vothqifia-bfidsetrestyexertin a yielding resistance against movement or the '3. The methodof weig tings; a multipleleg core part formed 01a plurality of layers of magnetic sheet steel positioned at right angles to a plane through theaxis'oLthe .c'ore legs and bonded .togetherto providev fiat surfaces for, cooperating with similar surfaces to form-a butt,- joint, comprising positioning, the yends of the core legs to be worked in engagement; with an abrasive surface moving in a plane ,and in ri dly support n the first has t beengagedby said abrasive suIfaceagainst-movement with the surface and in yielding 1y supporting-tl ie remaining: p rtion of the core p tfiflgainstwmovement with s I- 4. The method ofworking the end surfaces of a, U -shaped core: part rformed v of a plurality of layers of magnetic sheet steel positioned at,- right angles to Plane-through th the re legs bonde met ic? or v efiatsu tac f r c rat t similar; sur ce zf m a t Jo n com ri an iti ins theend he corellegs to be worked. in engagement withvan b a ve Surface m n ineman? anew ri idly supporting. the first leg to be tenga ed by; said abrasive surface against movement with the surface and in yieldingly. supporting the otherlo v rtt eam a asa timov en tw hthe sure core part when brought into engagement with the abrasive surface including a fixed rest forrigidly engaging one of said end portion adjacent the abrasive surface, and a rest for yieldingly engaging the other of said end portions.

6. Apparatus for working the surfaces of magnetic core structures formed of U-shaped core part having a plurality of layers of magnetic sheet steel positioned at right angles to a plane passing through the axes of the two leg portions thereof comprising a flat table top surface, an endless abrasive belt and means for moving the abrasive belt across the table top to provide a continuously moving fiat abrasive surface, bridge rests for supporting the end portions of the U-shaped core part when brought into engagement with the abrasive surface including a narrow restpositioned close to the abrasive surface between the end portion of the core and fixedly mounted to rigidly support the first of the two leg portions against movement with the abrasive belt, and a narrow rest positioned close to the abrasive surface and mounted to yieldingly support the other of said leg portions.

7 Apparatus for working the surfaces of magnetic structures formed of U-shaped core parts having a plurality of layers of magnetic sheet steel positioned at right angles to a plane passing through the axes of each of the two leg portions thereof comprising a fiat table topsurface, an endless abrasive belt and means for moving the abrasive belt across the table top to provide a continuously moving flat abrasive surface, bridge rests. for supporting the end portions of the U-shaped core part when brought into engagement with the abrasive surface including a nar row rest positioned close to the abrasive surface between the end portionsof the core and fixed-- ly mounted to rigidly support the first of the two leg portions against movement .with the abrasive belt and a narrow rest positioned close .to the abrasive surface and flexibly mounted to yieldingly support the other of said leg portions, and means for supplying water to the abrasive surface adjacent the two leg portions of the core part.

8. The method of working the outer end sur-' Q faces of core parts havinga plurality of core leg portions formed of a plurality of laminations of magnetic sheet steel positioned fiatwise and bonded together, the one upon the other comprising positioning the leg portions of the core parts in engagement with a movable flat grinding surface with the ends of the lamlnations in engagement with the grinding surface substantially at right angles to the direction of motion of the grinding surface and in rigidly supporting one leg .portion of the core closely adjacent to thegrinding surface to prevent movement of the supported leg portion with the grinding surface and in yieldably supporting the other leg portions of the core part to prevent movement of the supporting leg portion with the grinding surface.

9. The method of working the outer end surfaces of core parts having a plurality of core leg portions formed of a' plurality of laminations of magnetic sheet steel positioned flatwise and bonded together, the one upon the other comprising positioning the leg portions of the core parts in engagement with a movable flat grinding surface with the ends of the laminations in engagement with the grinding surface substantially at right" angles to the direction of motion of the grinding surface and in supporting the core portion by I exerting a rigid resistance against movement of one core leg portion and exerting a yielding re-.

sistance against movement of the other core leg portion. r

JOHN H. BRAMBLE. MICHAEL DUNN. 

